A femtocell base station corresponds to a type of base station, which corresponds to a small sized version of a macrocell base station that can perform most of the functions of the macrocell base station, and which may be installed in a cover area of the macrocell base station or in a shadow area that cannot be covered by the macrocell base station. The femtocell base station is equipped with a network configuration that can be independently operated. And, as compared to relay base stations, a remarkably larger number of femtocell base stations may be installed in downtown areas or indoor areas. Therefore, due to the large amount of information, a list of femtocell base stations is not included in a list of neighboring base stations, which is transmitted to the user equipment by the base station.
FIG. 1 corresponds to a structural view of a wireless communication system additionally including a femtocell base station.
As shown in FIG. 1, the wireless communication system additionally including a femtocell base station includes a femtocell base station (110), a macrocell base station (120), a femto network gateway (hereinafter referred to as “FNG”) (130), an access service network (hereinafter referred to as “ASN”) (140), and a connectivity service network (hereinafter referred to as “CSN”) (150). Herein, the macrocell base station (120) refers to a general base station that is included in the related art wireless communication system.
As a small sized version of the macrocell base station (120), the femtocell base station (110) performs most of the functions of the macrocell base station. The femtocell base station (110) directly accesses a TCP/IP (transmission control protocol/internet protocol) network and operates independently, just as the macrocell base station (120). Herein, the coverage of the femtocell base station (110) is within range of approximately 0.1˜30 m. And, one femtocell base station (110) may accommodate about 10˜20 user equipments. Herein, the femtocell base station (110) may either use the same frequency as that of the macrocell base station (120) or use a different frequency.
The femtocell base station (110) is connected to the macrocell base station (120) through an R1 interface, thereby being capable of receiving a downlink channel of the macrocell base station (120). And, the femtocell base station (110) may transmit a control signal to the macrocell base station (120).
The femtocell base station (110) is capable of covering indoor or shadow areas that cannot be covered by the macrocell base station (120) and may also support a high data transmission rate. The femtocell base station (110) may be installed within the macrocell in a overlay format, or the femtocell base station (110) may also be installed in a non-overlay format in an area that cannot be covered by the macrocell base station (120).
The femtocell base station (110) may be divided into two different types. A first type corresponds to a CSG (closed subscriber group) femtocell base station, and a second type corresponds to an OSG (open subscriber group) femtocell base station. The CSG femtocell base station groups user equipments that can access the CSG femtocell base station and assigns CSG ID (identification) to the accessing user equipments. Thereafter, only the user equipments that are assigned with a CSG ID can access the CSG femtocell base station. The OSG femtocell base station corresponds to a base station that allows the access of all user equipments.
The FNG (130) is a gateway that is configured to control the femtocell base station (110). Herein, the FNG (130) is respectively connected to the ASN (140) and the CSN (150) through an Rx interface and an Ry interface. The femtocell base station (110) may receive service from the CSN (150) through the FNG (130), and the user equipments that are connected to the femtocell base station (110) may be serviced with functions, such as certification, IMS, and so on, from the FNG (130) or the CSN (150).
The CSN (150) provides the user equipments with connections to application services, such as the internet, VoIP, and so on, and also provides the user equipment with certification (or authentication) and charging functions. And, the ASN (140) controls the macrocell base station (120) and manages the connection between the macrocell base station (120) and the CSN (150).
FIG. 2 illustrates an exemplary scheduling method of a related art macrocell base station.
The scheduling method shown in FIG. 2 corresponds to a case where a conventional macro based scheduling method is extended to a hierarchical cell structure. The conventional method corresponds to a method wherein the macrocell base station receives feedback information (e.g., channel information, traffic information) from macro users and authorizes communication through a specific frequency at a specific timing. Accordingly, when this method is extended and applied to a hierarchical cell structure, the macrocell base may receive all necessary information from the femto users and the macro users. At this point, the femto user may include a parameter respective to its relation with the femtocell base station in the feedback, rather than a parameter respective to its relation with the macrocell base station, and transmit the feedback information including the parameter respective to the relation between the femto user and the femtocell base station. After receiving the feedback information from the femto users and the macro users, the macrocell base station may allocate resource to each user. The macrocell base station may differentiate the macro users from the femto users and may operate accordingly.
Herein, in case of the macro users, the necessary information may follow the conventional method. And, in case of the femto users, the necessary information may be fed-back to the macrocell base station by using the conventional method, or the femtocell base station may gather information on the femto user and may feed-back the gathered information instead of the femto user. At this point, when the macrocell base station allocates femto user resources, this indicates that the femto user is authorized to perform communication with the femtocell base station by using the corresponding resource.
FIG. 3 illustrates a frame structure used by the related art macrocell base station for transmitting scheduling information.
The macrocell base station may transmit scheduling information to the macro users and the femto users in subframe units by using a macro PDCCH section. The related art scheduling method is disadvantageous in that the femtocell base station operates manually and performs operations similar to those of a relay station, and that free scheduling cannot be performed. Furthermore, the related art scheduling method is also disadvantageous in that a scheduling overhead of the macrocell base station is considerably high, and also that user equipments having poor reception from the macrocell base station cannot receive any scheduling information.